Why is ammonia removed from coke oven gas during the purification process?
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Why is ammonia removed from coke oven gas during the purification process? The reason given in the book is: (1) Ammonia is a good type of waste ； (2) Ammonia easily causes the washing oil of crude benzene to become emulsified and deteriorated ； (3) Ammonia has a severe corrosive effect on production equipment and gas pipelines. (1) and (2) are easy to understand. What’s unclear is (3): doesn’t ammonia cause corrosion in the gas collection pipes, intake pipes, and the pipes before the ammonium sulfate production section? Acidic corrosion of iron is essentially a displacement reaction; for example, with hydrochloric acid (HCl): Fe + 2HCl → FeCl2 + H2↑. So, how does NH3 corrode Fe?
The corrosion of gas pipelines by ammonia is mainly due to its tendency to form ammonium ions in humid environments, and ammonium ions are highly corrosive. When ammonia meets water vapor, hydrolysis occurs to produce ammonium hydroxide, which is an alkaline substance that can damage the protective layer on the surface of pipes, thereby leading to iron corrosion. Furthermore, the presence of ammonia can also promote the formation and action of other corrosive substances. Therefore, to ensure the safe operation of production equipment and gas pipelines, it is necessary to remove ammonia from coke oven gas as much as possible. .
Ammonia is alkaline, while benzene is an oil that tends to emulsify easily； Ammonia is present in gas; in alkaline gases, water and acidic substances such as HCN, H2S, and CO2 form condensates, which are primarily responsible for electrochemical corrosion
Ammonia becomes alkaline when dissolved in water. It will cause pitting corrosion of the metal. My personal understanding is that it’s a galvanic cell reaction.
Ammonia becomes more corrosive when combined with water, and this effect increases as the temperature rises. Now, the pipes behind many fans are also made of stainless steel. Additionally, when the benzene extraction unit is in operation, too much ammonia enters, which causes the temperature to drop; both the gas and the liquid are highly corrosive. If ammonia is not removed, the equipment used for benzene extraction suffers severe corrosion.